Many industrial operations that require heating solid material to high temperatures are carried out in kilns, wherein the material is fed into a kiln and passed through the kiln while the material is exposed to heat generated by combustion of fuel and oxidant within the kiln. The rate at which material can be processed in kilns can be increased by combusting the fuel with oxygen-enriched air or commercial-purity oxygen. However, combustion with oxidant that has such an increased oxygen content can produce increased amounts of environmentally undesirable byproducts such as nitrogen oxides that threaten to exceed regulatory limits on such emissions.
There remains a need for techniques to improve kiln operations in a way that can increase productivity without causing undue amounts of emissions such as nitrogen oxides.